+;;; Return T if the string S contains characters which need to be
+;;; escaped to print the symbol name, NIL otherwise.
+(defun escape-symbol-name-p (s &optional uppercase)
+ (let ((dots-only t))
+ (dotimes (i (length s))
+ (let ((ch (char s i)))
+ (setf dots-only (and dots-only (char= ch #\.)))
+ (when (or (terminalp ch)
+ (char= ch #\:)
+ (and uppercase (not (char= ch (char (string-upcase (string ch)) 0))))
+ (char= ch #\\)
+ (char= ch #\|))
+ (return-from escape-symbol-name-p t))))
+ dots-only))
+
+;;; Return T if the specified string can be read as a number
+;;; In case such a string is the name of a symbol then escaping
+;;; is required when printing to ensure correct reading.
+(defun potential-number-p (string)
+ ;; The four rules for being a potential number are described in
+ ;; 2.3.1.1 Potential Numbers as Token
+ ;;
+ ;; First Rule
+ (dotimes (i (length string))
+ (let ((char (char string i)))
+ (cond
+ ;; Digits TODO: DIGIT-CHAR-P should work with the current
+ ;; radix here. If the radix is not decimal, then we have to
+ ;; make sure there is not a decimal-point in the string.
+ ((digit-char-p char))
+ ;; Signs, ratios, decimal point and extension mark
+ ((find char "+-/._^"))
+ ;; Number marker
+ ((alpha-char-p char)
+ (when (and (< i (1- (length string)))
+ (alpha-char-p (char string (1+ i))))
+ ;; fail: adjacent letters are not number marker, or
+ ;; there is a decimal point in the string.
+ (return-from potential-number-p)))
+ (t
+ ;; fail: there is a non-allowed character
+ (return-from potential-number-p)))))
+ (and
+ ;; Second Rule. In particular string is not empty.
+ (find-if #'digit-char-p string)
+ ;; Third rule
+ (let ((first (char string 0)))
+ (and (not (char= first #\:))
+ (or (digit-char-p first)
+ (find first "+-._^"))))
+ ;; Fourth rule
+ (not (find (char string (1- (length string))) "+-)"))))
+
+#+nil
+(mapcar #'potential-number-p
+ '("1b5000" "777777q" "1.7J" "-3/4+6.7J" "12/25/83" "27^19"
+ "3^4/5" "6//7" "3.1.2.6" "^-43^" "3.141_592_653_589_793_238_4"
+ "-3.7+2.6i-6.17j+19.6k"))
+
+#+nil
+(mapcar #'potential-number-p '("/" "/5" "+" "1+" "1-" "foo+" "ab.cd" "_" "^" "^/-"))
+
+(defun escape-token-p (string &optional uppercase)
+ (or (potential-number-p string)
+ (escape-symbol-name-p string uppercase)))
+
+;;; Returns the token in a form that can be used for reading it back.
+(defun escape-token (s &optional uppercase)
+ (if (escape-token-p s uppercase)
+ (let ((result "|"))
+ (dotimes (i (length s))
+ (let ((ch (char s i)))
+ (when (or (char= ch #\|)
+ (char= ch #\\))
+ (setf result (concat result "\\")))
+ (setf result (concat result (string ch)))))
+ (concat result "|"))
+ s))
+
+(defvar *print-escape* t)
+
+(defun write-to-string (form)